A brief introduction to the principle and method of diffusion test of microporous filtration membran

Diffusion test, also known as diffusion flow test, is a common method for evaluating the performance of microporous filtration membranes. It mainly measures the ability of microporous membranes to prevent the passage of liquids exceeding a certain size threshold while allowing specific gases or vapors to pass through. The concept It sounds a bit mouthful, its test principle is based on the concept of diffusion, that is, the passage of gas molecules moving from the high concentration area through the filter membrane to the low concentration area, because it is a quantitative value, not only can accurately determine the integrity of the membrane , and can also reflect the porosity, flow rate and effective filtration area of the membrane and other indicators.

The following is a general procedure for performing a diffusion test on a microporous filtration membrane:

1. Membrane sample selection and preparation, select a suitable microporous membrane material compatible with the substance to be tested, cut the membrane into the required shape and size, and ensure that the membrane does not have any defects or irregularities that may affect the diffusion measurement, and at the same time To ensure the cleanliness of the membrane, it is necessary to remove any pollutants or residues that may interfere with the diffusion test. The method of cleaning can be carried out according to the nature of the membrane material and pollutants. It is very important for us to pretreat the membrane before the test to stabilize its performance. , which can effectively guarantee the effect of the test.

2. Setting of test equipment, test liquid, diffusion test equipment usually consists of a diffusion cell or a diffusion chamber, a gas source, a pressure regulator and a pressure gauge. The chamber is divided into two compartments separated by a membrane to be tested. One compartment is connected to an air source, while the other compartment is open to atmosphere. Commonly used test fluids are usually water for hydrophilic membranes and alcohol/water mixtures for hydrophobic membranes.

3. Adjust the sample. Before the test, the film sample needs to be adjusted to ensure that it reaches a stable state. The film sample is pre-wetted and installed on the test equipment, and the equipment is adjusted according to the test conditions and required standards.

4. At the beginning of the test, the pressure of the filter membrane can be slowly increased to the recommended test pressure provided by the manufacturer, usually at least 80% of the minimum bubble point specification, and the pressure regulator is adjusted to provide a constant air flow across the membrane surface. The flow rate is usually at Specified in the test method or standard book. After the balance is stable, the timing test is performed, the gas is fully diffused through the membrane, and the flow value of the gas entering and leaving the membrane is recorded.

5. Results data analysis. After the test duration is over, collect and analyze the gas on the downstream side of the membrane to determine the concentration or amount of gas diffused through the membrane. Depending on the nature of the gas to be measured, gas chromatography or spectrophotometry can be used; Finally, the collected data is analyzed to calculate parameters such as the diffusion rate or permeability of the membrane, while comparing with standard requirements. Through the method of taking the average value of multiple measurements, when the measured value is found to exceed the required standard value, it can be determined from the pore size, temperature and ambient temperature settings, membrane wetting, membrane or seal integrity, liquid/gas combination and recommended liquid compliance Factors such as stability and stability time were analyzed.

We use the diffusion method for membrane testing, which is subject to the judgment of the specific test setup and procedure, and the process and steps may vary depending on the intended application, the type of membrane being tested, and relevant industry standards or guidelines, and the applicator is advised It is essential to refer to the appropriate test method or standard to ensure the accuracy and consistency of the test.